The present invention relates to a method for adaptive control of distance and/or driving speed of a motor vehicle. Control systems of the species are, for example, also known as adaptive cruise control systems (ACC systems).
An ACC system based on radar is known from SAE paper 961010 (SAE Technical Paper Series 961010, International Congress and Exposition, Detroit, Feb. 26-29, 1996, xe2x80x9cAdaptive Cruise Control Systemxe2x80x94Aspects and Development Trendsxe2x80x9d, Winner, Witte, Uhler, Lichtenberg, Robert Bosch GmbH). In this case, the radar sensor having multiple target capability is mounted at the front end of a motor vehicle, in order to determine distances from and speeds relative to vehicles driving ahead. The data ascertained by the radar system is supplied to a control unit via a bus system. Using the transmitted radar data and the wishes of the driver, this control unit determines an appropriate acceleration request which, in turn, is transmitted to a longitudinal control unit. The longitudinal control unit controls actuators in accordance with the acceleration request of the control unit. These actuators can be the engine of the motor vehicle, the clutch, or the brakes of the motor vehicle. The corresponding control of the actuators produces a certain behavior of the motor vehicle, which, in turn, is fed back to the control unit, thus forming a control loop. Either the drive train or the brakes are activated as a function of the corresponding acceleration request. The estimated slope of the road is considered in this selection. In addition, the limitations, i.e. physical limitations of the drive train and the braking system, must be known or appropriately calculated.
A method for the adaptive control of distance and/or driving speed of a motor vehicle, where a control device can control an engine of the motor vehicle at least in a first operating mode and a brake of the motor vehicle in a second operating mode, is first of all (first method) further refined in that a quantity (aSetpoint) representing a setpoint deceleration or a setpoint acceleration is determined, and in that, when operating in the first operating mode, a transition is made to the second operating mode when quantity (aSetpoint)is within a predefinable range of values.
Secondly (second method), the method is further refined in that a transition is made to the first operating mode when the brake essentially has no decelerating effect.
The result of these two methods of the present invention is that the transition from the first operating mode in which the engine, i.e. the drive of the motor vehicle is controlled to the second operating mode in which the brake of the motor vehicle is controlled, and vice versa is carried out comfortably without any noticeable jerking for the driver of the motor vehicle. The method according to the present invention further achieves that unnecessary brake control and corresponding flickering of the brake lights are prevented.
The first described method is advantageously further refined in that the specifiable range of values is determined as a function of a quantity (aDrag) representing a drag torque of the engine, and in that the specifiable range of values includes all values below a threshold value (aThreshold). In this context, it is particularly advantageous when threshold value (aThreshold) is formed by subtracting a quantity (aHysteresis) representing a hysteresis from a quantity (aDrag) representing the drag torque. As a result of these further refinements of the first method of the present invention, a threshold value (aThreshold) is formed for the transition from the engine to the brake mode, which takes a certain hysteresis value into consideration in addition to the drag torque of the engine. As a result, it is achieved in a particularly advantageous manner that there is no xe2x80x9cflickering switchingxe2x80x9d between the control of the engine and the control of the brake.
A preferred further refinement of the first method according to the present invention provides that, starting from a determinable instant (TBrake), quantity (aHysteresis) representing the hysteresis decreases linearly over time (t) from a maximum value (aHysteresisMax) to a minimum value (aHysteresisMin). In this context, determinable instant (TBrake) is advantageously selected in such a manner that this is the instant at which quantity (aSetpoint) representing a setpoint deceleration or a setpoint acceleration is less than quantity (aDrag) representing a drag torque. This further refinement achieves that, starting from the instant from which the ACC control device supplies an acceleration request (aSetpoint) to longitudinal controller (LOC) that is less than drag torque (aDrag) of the engine, hysteresis value (aHysteresis) is continuously decreased. As a result, it is further achieved that in the case in which acceleration request (aSetpoint) has a constant value that is less than quantity (aDrag) representing the drag torque of the engine or than the drag torque of the engine, a conversion to the brake mode, i.e., the second operating mode, is carried out at the latest when quantity (aHysteresis) representing the hysteresis has decreased to minimum value (aHysteresisMin). A particularly advantageous design of the slope with which quantity (aHysteresis) representing the hysteresis linearly decreases over time provides that the slope is proportional to the difference of quantity (aSetpoint) representing the setpoint deceleration or the setpoint acceleration and quantity (aDrag) representing the drag torque. This design of the slope results in a particularly advantageous manner in a highly dynamic response characteristic. In particular, when the driver of the motor vehicle desires a particularly sharp deceleration, i.e., strongly operates the brake pedal, for instance, the design of the slope according to the present invention leads to a quick transition to the braking branch. As a result of high setpoint deceleration request (aSetpoint) being present, quantity (aHysteresis) representing the hysteresis is quickly reduced in the direction of minimum value (aHysteresisMin) Depending on the form of minimum hysteresis value (aHysteresisMin), a direct transition from the drive branch to the braking branch can occur in an extreme case.
Another advantageous further refinement of the first method provides that quantity (aDrag) representing a drag torque is determined as a function of the slope of the road on which the motor vehicle is traveling. For this purpose, a slope estimation, which, is performed particularly after a braking action, can advantageously be carried out in a rapid method. Such a rapid method can be carried out, for example, for a slope estimation using at least one quantity representing an engine output torque and one quantity representing an actual acceleration of the motor vehicle. As a result of this advantageous embodiment, it is possible to estimate the slope at every instant at which there is no braking action. In particular, this embodiment is significant when the vehicle is traveling on roads having significant uphill and downhill grades, e.g. in the mountains, because the influence of the gradient of the road on quantity (aDrag) representing a drag torque is particularly great in this instance.
The preferred further refinement of the second method provides that the brake makes available an appropriate signal (NoBrake) on a bus system (CAN bus) when no more decelerating effect is present. In the case of an active brake, this can, for example, be a self-diagnosis unit integrated in the braking system that then provides the appropriate signal on the CAN bus when essentially no more decelerating action is present. The control device present in the motor vehicle according to the second method can, in this case, access the CAN bus and extract the appropriate signal in order to carry out the appropriate method. The method can be further refined in that in the case in which the appropriate signal (NoBrake) from the brake is not present within a predetermine time (TNoBrake), a direct transition is made to the first operating mode. In practice, this means that when the brake is no longer being actively controlled, a certain amount of time is allowed to elapse to determine whether the pressure of the active brake or the decelerating action can be reduced. If this is not the case after a certain amount of time, possible wear of the brake is accepted, and the drive train or the engine is accordingly controlled despite the still present decelerating action.
As a result of the embodiment of the second method of present invention, the transition from the second operating mode, i.e., the braking condition, to the operating mode, i.e., the drive mode, is decidedly improved. This embodiment is particularly important since in the case of active brakes, the built up braking pressure is first decreased again. This means that an active brake still has a decelerating effect for a short transition region when the brake is no longer being controlled. To minimize the wear of the active brake in these special operating states, it is particularly advantageous according to the second method of the invention that a transition is first made to the drive mode (first operating mode) when the brake (active brake) essentially exhibits no more decelerating action. This ensures a jerk-free, quick transition between the brake mode and the drive mode.